1. Field of the Invention
The present invention relates to a ceramic substrate and manufacturing method thereof; and, more particularly, to a ceramic substrate having a hole, which is formed in a ceramic layer of being a surface layer in a ceramic stacked layer structure to expose a via and is filled with a conductive paste, and manufacturing method thereof.
2. Description of the Related Art
In line with the recent trend toward miniaturization of an electronic parts, much development for fine-patterning, precision, and thinness has been achieved even in a module and a substrate. However, in the case where a widely used PCB (Printed Circuit Board) is applied in miniaturized electronic parts, there has been many problems such as size's miniaturization, signal loss in a high frequency domain, and reduction in reliability at the time of high temperature and high humidity.
In order to overcome such problems, a ceramic-based substrate has been used instead of a PCB substrate. A main component of the ceramic substrate corresponds to a ceramic composition which contains a large amount of glass capable of low-temperature co-firing.
There exist various methods for manufacturing an LTCC (Low Temperature Co-fired Ceramic) substrate, which may be classified into shrinking and zero-shrinking according to whether or not the ceramic substrate is shrunk during a firing process. In particular, a method for manufacturing the ceramic substrate to be shrunk in firing refers to shrinking. However, in the case of the shrinking, non-uniform shrinkage occurs in the ceramic substrate, so dimensional change is produced along a surface direction of the substrate. Such shrinkage of the ceramic substrate in a surface direction causes deformation of patterns of a printed circuit included in the substrate, which results in deterioration of precision of pattern's position and disconnection of the patterns. Therefore, in order to solve the problems, zero-shrinking has been proposed that can prevent the ceramic substrate from being shrunk in the surface direction.
Herein, the zero-shrinking refers to a method for forming a constrained layer on the both surfaces of the ceramic substrate and firing the formed substrate. In this case, the constrained layer may be formed of a material, which is suitable for shrinkage control while allowing the substrate not to be shrunk at a temperature where the ceramic substrate is fired. Such a constrained layer allows the ceramic substrate to be shrunk only in a thickness direction while preventing the ceramic substrate from being shrunk in the surface direction, at the time of the firing.
In the case where a ceramic substrate is manufactured by employing the conventional zero-shrinking, it is possible to suppress shrinkage of the substrate in the surface direction when fired. However, in the case of a via vertically connected for interlayer-connection, the via fails to coincide with behavior of the LTCC firing, and constraint force for suppressing shrinkage of the substrate in the surface direction is difficult to apply, which results in defects of the substrate. In particular, in the case of a structure where defects around the via are exposed to a surface layer, the defects cause packaging-failure at the time of forming external patterns. That is, the defects around the via are provided in various forms such as voids, cracks, projection, depression, and so on, which causes packaging-failure and reliability-deterioration, such as wire bonding, an SMT, soldering, and so on.